The present invention relates to high speed dot matrix impact printers and, more particularly, to the structure of a printer arm actuated by an electromagnet for selectively operating wire stylus of a wire matrix print head.
Well-known wire matrix print heads generally have a plurality of wire styli arranged in matrix, and armatures and electromagnets are arranged correspondingly to these wire styli. In accordance with the dot pattern of a character to be printed, the electromagnets are selectively actuated so that desired wire styli are actuated through the armatures to thereby exert an impact on the printing paper through an ink ribbon to print on the printing paper a character, a symbol or a pattern comprising a dot assembly.
In this type of wire matrix head, there is a great demand for higher printing speed and, to the end, various efforts are being made to increase the speed of operation of the electromagnet or the armature. It is well known that the fundamental and effective measure to increase the printing speed is to reduce the moment of inertia of the armature in rotation around its supporting point without reducing the electromagnetic attracting force.
In another well-known method for reducing the moment of inertia of an armature as disclosed in U.S. Pat. No. 4,136,978, the armature is divided into a magnetic member and an actuator, and the actuator is made of a thin sheet material in a hollow configuration.
In order to further reduce the weight of the actuator or armature, it has been proposed to form one or more holes in the side walls of the armature lever. The thinning of the actuator or armature lever, as well as the formation of holes, for reducing the weight inconveniently causes a reduction of rigidity of the armature lever, often resulting in a lateral vibration of the side wall of the armature lever.